lua

2.6 – Functions

Functions are first-class values in Lua. That means that functions can be stored in variables, passed as arguments to other functions, and returned as results. Such facilities give great flexibility to the language: A program may redefine a function to add new functionality, or simply erase a function to create a secure environment when running a piece of untrusted code (such as code received through a network). Moreover, Lua offers good support for functional programming, including nested functions with proper lexical scoping; just wait. Finally, first-class functions play a key role in Lua's object-oriented facilities, as we will see in Chapter 16.

programming in Lua

6.1 – Closures

6.3 – Proper Tail Calls